1. Field of the Invention
The present invention generally relates to thin film inductive read-write heads for use in magnetic storage systems. More particularly, the present invention is directed to high throughput methods for the rapid production of thin film inductive read-write heads having very narrow write track widths, to inductive read write heads so produced, and to the associated apparatus and methods for their use.
2. Description of Related Art
In magnetic disk drives, data is written and read by magnetic transducers called xe2x80x9cheads.xe2x80x9d The magnetic disks are rotated at high speeds, producing a thin layer of air called an air bearing surface (ABS). The read and write heads are supported over the rotating disk by the ABS, where they either induce or detect flux on the magnetic disk, thereby either writing or reading data. Layered thin film structures are typically used in the manufacture of read and write heads. In write heads, thin film structures provide high areal density, which is the amount of data stored per unit of disk surface area, and in read heads they provide high resolution.
A thin film write head comprises two pole pieces, a top pole piece P1 and a bottom pole piece P2. A write head generally has two regions, denoted a pole tip region and a back region. The pole pieces are formed from thin magnetic material films and converge in the pole tip region at a magnetic recording gap, known as the zero throat level, and in the back region at a back gap. The zero throat level delineates the pole tip region and back region. A write head also has two pole tips, P1T and P2T, associated with and extensions of P1 and P2 respectively. The pole tips, which are relatively defined in their shape and size in contrast to the pole pieces, are separated by a thin layer of insulation material such as alumina, referred to as a gap. As a magnetic disk is spinning beneath a write head, the P2 pole tip trails the P1 pole tip and is therefore the last to induce flux on the disk. Thus, the P2T dimension predominantly defines the write track width of the write head, and is generally considered an important feature.
The write track width, P2B, is especially important because it limits the areal density of a magnetic disk. A narrower track width translates to greater tracks per inch (TP1) written on the disk, which in turn translates to greater areal density. However, with present manufacturing methods for read-write heads, the ability to produce very narrow track widths is limited. These limitations will be further explained with reference to a specific type of inductive head. Inductive heads commonly employed at present are magnetoresistive (MR) sensors, which are highly sensitive to changes in magnetic flux on a disk written by inductive write heads. An MR sensor comprises a thin film layer sandwiched between bottom and top insulation layers, or gaps, which are in turn sandwiched between bottom and top shield layers, S1 and S2. An MR head can read information on a magnetic disk with much narrower track widths an much higher fidelity than other known types of read heads. The apparent ability of MR sensors to read very narrow track widths may enable the use of narrow track width write heads and therefore lead to high areal densities. While this advantage has been sought through the use of photoresist frame plating and ion beam milling of write heads, manufacturing heads with very narrow P2B track widths remains a significant challenge.
A particular type of MR head is a merged MR head. A merged MR head uses the top shield S2 of the MR head as the bottom pole P1 of the write head. Thus, this layer is shared by each of the read and write heads. While merged MR heads have a high capacity for both reading and writing, they are limited in the narrowness of the track width they may utilize because they have been found to possess large side-fringing fields during recording. These fields are caused by differences in P1T and P2T widths. The fringing field, caused by flux leakage from P2 to P1 beyond the width of P2, is the portion of the magnetic field which extends toward the tracks adjacent to the tracks being written. The fringing fields require lower TP1 in order not to impinge adjacent tracks, thereby limiting the achievable areal density.
Prior art practitioners have sought to reduce fringing fields in merged MR heads. Typically, this involves manufacturing heads with vertically aligned P1T and P2T side walls. A method exemplary of one which addresses this issue is found in U.S. Pat. No. 5,438,747, entitled xe2x80x9cMethod of Making a Thin Film Merged MR Head With Aligned Pole Tips,xe2x80x9d incorporated herein by reference. Manufacturing techniques directed to achieving P1 and P2 pole tips of substantially similar widths do effectively reduce the fringing field. However, they may be unfortunately limiting in their ability to produce substantially narrow P2B track widths. Therefore, while the capacity for high areal density is preserved through manufacturing methods which are aimed at reduction of fringing fields, it may actually be hampered by those same manufacturing methods which place an undesirable lower limit on the size of P2B write head track width. Furthermore, they produce an additional manufacturing burden in the form of cleanup of redeposited material, which translates to greater time and higher production costs.
Other MR head manufacturing methods have addressed the issue of reducing the write track width. An example is U.S. Pat. No. 5,726,841 entitled, xe2x80x9cThin Film Magnetic Head With Trimmed Pole Tips Etched by Focused Ion Beam for Undershoot Reduction,xe2x80x9d incorporated herein by reference. While the use of a focused ion beam tool (FIB) may effectively produce a narrow P2B track width, the technique would be performed a separate time for each head. In typical manufacturing processes which develop more than 20,000 heads per wafer, use of FIB is not feasible.
As previously mentioned, other methods for manufacturing heads with vertically aligned pole tip side walls include forming the P2 pole tip either by photoresist frame plating or ion beam milling. In these cases, the P2T is plated with additional thickness as it is used as a mask during the processing which trims the pole tip width, removing pole tip thickness in the process. Sufficient pole tip thickness must be retained throughout the milling process for a pole tip to have a suitable aspect ration. Aspect ratio is the thickness/width of a pole tip, and should generally be greater than about 2. The width of the pole tip P2B that may be fabricated by present methods is limited, then, by the amount of pole tip thickness that may be lost during pole tip width milling. This, and other limitations inherent to current manufacturing technology, reates significant challenges in the production of very narrow pole tip read/write heads.
It is a purpose of the present invention to improve the current limitations known in read-write head track widths incurred by practical limitations of current manufacturing methods. Specifically, an object of the present invention is to improve write head track width by nearly an order of magnitude.
The invention utilizes a preliminary milling step before standard P1 notching in order to create a P2B track width that is substantially sub-micrometer and narrower than that which could previously be realized. Larger amounts of P1 material may then be removed during P1 milling procedures, the write track dimension having already been reduced.
It is a further object of the invention to produce the narrow write track heads by a method that enables high throughput manufacturing. A preliminary milling step may be utilized on a wafer in a high throughput manufacturing system, wherein the write track width P2B may be milled to a very narrow dimension before it is divided into multiple heads. The invention thereby enables a novel application of a preliminary precision milling step to substantially reduce the write track width of many heads on a single substrate.
The preliminary milling step of the present invention occurs before standard P1 notching. It employs a wafer manufacturing process such as ion beam milling to perform P2 pole trimming and mill the write track width prior to P1 notching. The write track width is milled at an angle, preferably 45xc2x0 to 85xc2x0 from the wafer normal, effecting a precise removal of material. As used in this specification, the term xe2x80x9cwafer normalxe2x80x9d refers to a direction substantially perpendicular to the plane in which the wafer is oriented. The precision P2B milling may then be followed by less prccise, conventional P1 milling, which provides alignment of P1T and P2T sidewalls for reduction of fringing fields.
The present invention, therefore, yields several surprising advantages over the prior art. A thin film inductive read write head manufactured according to a method exemplary of the invention will have a write track significantly less than that which has been previously known. This will yield a substantial increase in the areal storage of magnetic disk drives. Furthermore, the present invention enables high throughput manufacturing systems for producing large quantities of the narrow write track inductive heads.
The foregoing and other objects, features, and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments which makes reference to several drawing figures.